In the case of wooden panels, for example, to prevent the grain of the wood being visible after painting, it is important to carry out a careful sanding, sometimes also defined as super-finishing when its results approach those obtained with polishing.
Even with materials other than wood, such as for example Corian® or the like, which is frequently used in the preparation of kitchen worktops, it is necessary, after the sanding operation, in order to eliminate any small dips produced during that step, to carry out by hand a finishing step using hand tools.
Belt sanding machines are normally used in order to carry out this surface finishing of the panels, wherein, precisely in known manner, an abrasive belt is looped around suitable rollers for moving around them and engaging in sliding contact with the surface of a panel for modifying the appearance.
During the looped rotation of the belt about the relative drive and operating rollers the panel, normally located beneath the belt, is in turn moved along a rectilinear direction at a predetermined speed in such a way as to engage with the abrasive belt for a predetermined length of time.
The belt sanding machines of known type are not without drawbacks.
In effect, in the prior art belt sanding machines, considering a generic point of the surface of a panel, during the movement of the panel through the machine it normally engages with the belt having a peripheral speed parallel to that of panel itself.
This circumstance implies that with an imperfection present on the belt, the repeated passing over the same part of the panel can generate undesired alterations to its surface continuity, such as, for example grooves or lines.
A further drawback linked to the use of prior art sanding machines is that it is not possible to effectively process, with homogeneous results, panels or other elements consisting of wooden parts having different grain orientations, such as, for example, frames of doors and windows or the like. In fact, considering for example a wooden window, this has slats positioned at right angles to each other which, when they engage with the sanding belt are conditioned differently: the portions with a grain orientation parallel to the feed direction of the belt will in effect be more worn by the abrasive action of the belt than those with a grain orientation at right angles. This disparity of the effects makes manual sanding of the products suitable with consequent increases in the production times and costs.
There are prior art sanding machines wherein the trestle supporting the sanding belt can be oriented about a vertical axis in such a way that the feed direction of the belt is inclined at a predetermined angle relative to the feed direction of the panel being processed.
Examples of such machines are illustrated in patents WO 2004/009290 and DE 1 995 881.